A transparent item of a predetermined size that permits unobstructed and undistorted view of a desired area. It may include a frame, have reference markings, grid lines and may be heat strengthened and/or tinted. It is generally used where safety, security, and/or the restriction of foreign matter are required, such as the visual examination of the inside of pressurized tanks, liquid sights, controlled liquid flow, and inspection of equipment enclosed in a housing. See WINDOW (as modified); SCALE, CATHODE RAY TUBE; SCALE, PLOTTING; WINDOW, METAL; WINDOW, WOOD; and WINDOW PANEL, AIRCRAFT.